High refractive index phenol-modified siloxanes

ABSTRACT

Novel phenyl-modified phenol-modified siloxanes having at least a 50 weight percent aromatic content are disclosed and found to exhibit improved refractive index. A hydrosilation reaction process of preparing such modified siloxanes is also disclosed.

This is a continuation of Ser. No. 80/288,133 field Sep. 9, 1994 nowabandoned, which is a continuation of Ser. No. 08/146,349 filed Oct. 29,1993 also now abandoned which is a divisional of Ser. No. 07/934,046filed Sep. 21, 1992 now issued U.S. Pat. No. 5,272,013.

The present invention relates to phenol-modified siloxanes. Moreparticularly, the present invention relates to phenol-modifiedaryl-modified siloxanes having a high refractive index.

BACKGROUND OF THE INVENTION

Siloxanes having high refractive index are useful in many applications,including coatings for optical devices, such as contact lenses.Travnicek, U.S. Pat. No. 4,114,993 discloses a method for coatingcontact lenses comprising applying to the lens a coating of (i) apolymer of a dimethyl siloxane, a diphenyl siloxane or phenyl-methylsiloxane or both, and a vinyl siloxane; (ii) a polymer of a dimethylsiloxane, a diphenyl siloxane or phenyl-methyl siloxane or both, and analkyl hydrogen siloxane; and (iii) 5 to 20% fume silica.

Other disclosures of silicones for use in optical glass applications,include the Broer et al. patents, U.S. Pat. Nos. 4,718,748 and4,738,509, which describe an optical glass fiber having a syntheticresin cladding in which the first layer of the synthetic resin claddingis formed from a curable synthetic resin composition comprising acurable polysiloxane composition.

It has now been discovered that a new class of high refractive siloxanesare provided by incorporating aryl-modified siloxy units into arelatively low refractive index phenol-modified siloxane. These novelphenol-modified aryl-modified siloxanes surprisingly exhibit excellentoptical properties making them suitable for use in many applicationsrequiring materials having a high refractive index.

SUMMARY OF THE INVENTION

According to the present invention there is provided a siloxane havinghigh refractive index comprising a siloxane of the general formula:

    m'D.sub.x D'.sub.y M'

wherein M' represents a phenol-modified dialkyl siloxy group or anaryl-modified dialkyl siloxy group, D represents a dialkyl siloxy groupand D' represents a phenol-modified alkyl siloxy group or anaryl-modified alkyl siloxy group, provided said siloxane comprises bothphenol-modified and aryl-modified siloxy groups, x is above about 1 andy is above about 1.

Also according to the present invention there is provided a process forpreparing the aryl-modified phenol-modified siloxanes of the presentinvention comprising: (a) preparing a hydride silicone fluid of thegeneral formula: M^(H) D_(x) M^(H) wherein M^(H) represents an dialkylhydrogen siloxy, D represents a dialkyl siloxy and x is above about 1;(b) reacting the hydride silicone fluid of step (a) with a phenol toproduce a phenol-modified siloxane of the general formula: M^(Ph) D_(x)M^(Ph) wherein M^(Ph) represents a phenol-modified dialkyl siloxy, and Dand x are as defined above; (c) reacting the phenol-modified siloxane ofstep (b) with alkyl hydrogen cyclic siloxanes to produce aphenol-modified hydride silicone fluid of the general formula: M^(Ph)D_(x) D^(H) _(y) M^(Ph) wherein D^(H) represents an alkyl hydrogensiloxy, y is above about 1, and M^(Ph), D and x are as above-defined;and (d) reacting the phenol-modified hydride silicone fluid of step (c)with an aromatic compound to produce a aryl-modified phenol-modifiedsiloxane having high refractive index of the general formula: M^(Ph)D_(x) D^(Ar) _(y) M^(Ph) wherein D^(Ar) represents aryl- modified alkylsiloxy, and M^(Ph), D, x and y are as above-defined.

The present invention also provides an alternative process for preparingthe aryl-modified phenol-modified siloxanes of the present inventioncomprising: (a) preparing a hydride silicone fluid of the generalformula: M^(H) D_(x) D^(H) _(y) M^(H) wherein M^(H) represents a dialkylhydrogen siloxy, D represents a dialkyl siloxy; D^(H) represents analkyl hydrogen siloxy; x is above about 1; and y is above about 1; (b)reacting the hydride silicone fluid of step (a) with a relatively smallamount of a phenol to produce a phenol-modified hydride siloxane of thegeneral formula: M"D_(x) D"_(Y) M" wherein each M" independentlyrepresents either a dialkyl hydrogen siloxy or a phenol-modified dialkylsiloxy; each D" independently represents either an alkyl hydrogen siloxyor a phenol-modified alkyl siloxy, provided there are both hydrogensiloxy groups and phenol-modified siloxy groups in the phenol-modifiedhydride siloxane; and D, x and y are as defined above; and (c) reactingthe phenol-modified hydride siloxane fluid of step (c) with an aromaticcompound to produce a aryl-modified phenol-modified siloxane having highrefractive index of the general formula: M'D_(x) D'_(Y) M' wherein eachM' independently represents a phenol-modified dialkyl siloxy group or anaryl-modified dialkyl siloxy group; each D' independently represents aphenol-modified alkyl siloxy group or an aryl-modified alkyl siloxygroup, provided the aryl-modified phenol-modified siloxane comprisesboth phenol-modified and aryl-modified siloxy groups, and D, x and y areas above defined.

The present invention further provides a method of improving therefractive index of a phenol-terminated siloxane comprising (i) reactinga phenol-terminated siloxane of the formula M^(Ph) D_(x) M^(Ph) whereinM^(Ph) represents a phenol-modified dialkyl siloxy, D represents adialkyl siloxy group and x is above about 1; with alkyl hydrogen cyclicsiloxanes to produce a phenol-terminated hydride silicone fluid of thegeneral formula: M^(Ph) D_(x) D^(H) _(y) M^(Ph) wherein D^(H) representsan alkyl hydrogen siloxy, y is above about 1, and M^(Ph), D and x are asabove-defined; and (ii) reacting the phenol-terminated hydride siliconefluid of step (i) with an aromatic compound to produce an aryl-modifiedphenol-terminated siloxane having high refractive index of the generalformula: M^(Ph) D_(x) D^(Ar) _(y) M^(Ph) wherein D^(Ar) represents anaryl-modified alkyl siloxy, and M^(Ph), D, x and y are as above-defined.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides novel aryl-modified phenol-modifiedsiloxanes having excellent refractive index properties. These novelsiloxanes are useful in producing articles having improved opticalqualities.

The aryl-modified phenol-modified siloxanes have the general formula

    M'D.sub.x D'.sub.y M'

wherein M', D, D', x and y are as defined above.

In preferred embodiments of the present invention M' represents a phenoldialkyl siloxy of the general formula ##STR1## where R_(a) represents analkylene group, preferably of from 2 to about 12 carbon atoms, Y isselected from hydrogen, hydrocarbyl, hydrocarbyloxy and halogen, and Ris an alkyl group of from 1 to about 10 carbon atoms. A particularlypreferred phenol dialkyl siloxy useful in the practice of the presentinvention is a eugenol-modified dialkyl siloxy of the formula: ##STR2##where R is methyl.

The dialkyl siloxy units, D, of the present invention represent those ofthe general formula R₂ Sio-- wherein R is an alkyl of 1 to 10 carbonatoms, preferably methyl.

The preferred aryl modified alkyl siloxy groups of the present inventionare those where D^(Ar) is of the general formula RR^(Ar) SiO-- wherein Ris an alkyl of 1 to 10 carbon atoms, preferably methyl; and R^(Ar)represents a monovalent aralkyl radical, including but not limited tophenylethyl, styryl, α-methyl styryl, and the like. Preferably R^(Ar) isa phenylisopropyl group or a phenethyl group.

The values of x and y may vary greatly depending upon the desired endviscosity of the polymers of the present invention. Typically, x isabove about 1, preferably from about 1 to about 1000, more preferablyfrom about 1 to about 500, and most preferably from about 5 to about 50.Typically, y is above about 1, preferably from about 1 to about 2000,more preferably from about 1 to about 1000, and most preferably fromabout 10 to about 100.

The aryl-modified phenol-modified siloxanes of the present inventionprovide improved refractive properties. In preferred embodiments, thetotal aromatic weight content, including the aryl and phenol, of thearyl-modified phenol-modified siloxanes of the present invention isabove about 50 weight percent. Thus, in preferred embodiments of thepresent invention, the ratio of the values of y to x are above about2:1.

The aryl-modified phenol-modified siloxanes of the present inventiontypically have a refractive index of greater than about 1.5000 and caneasily be formed into articles of excellent optical quality by formingmethods known to those of ordinary skill in the art.

In a preferred embodiment, the aryl-modified phenol-modified siloxanesare prepared by a method generally comprising the steps of hydride fluidsynthesis; phenol hydrosilation; phenol hydride fluid synthesis; andaryl hydrosilation.

Accordingly, phenol end-capped siloxanes are synthesized by firstpreparing a hydride fluid from suitable precursors, such as alkyltetramers, in the presence of an acid catalyst, such as carbon black orsulfuric acid or mixtures thereof, according to acid equilibrationmethods known to those skilled in the art. The acid equilibration isthen followed by hydrosilation with a phenol, such as eugenol, in thepresence of a platinum catalyst, concluded with light-endsdevolatilization. Any of the known hydrosilation catalysts may be usedin the hydrosilation reaction. These are well described in the patentliterature, including, e.g., Lamoreaux, U.S. Pat. No. 3,220,972,Karstedt, U.S. Pat. Nos. 3,715,334, 3,775,452 and 3,814,730; and Ashby,U.S. Pat. Nos. 4,421,903 and 4,288,345.

Phenol hydride fluids are then synthesized from the phenol-end cappedsiloxanes by standard acid equilibration techniques. The phenol hydridefluids are then reacted with an aromatic compound following conventionalhydrosilation techniques. Any monovalent aromatic compound may be usedin the aromatic hydrosilation reaction, including, but not limited tostyrene compounds such as a-methyl styrene, styrene; etc. A particularlyuseful monovalent aromatic compound is α-methyl styrene.

It is also contemplated that the aromatic hydrosilation reaction may beperformed in the presence of solvents, such as toluene, or may be runneat (without solvent) as in other conventional hydrosilation reactions.

Alternatively, the aryl-modified phenol-modified siloxanes of thepresent invention may be prepared by a process generally comprising thesteps of hydride fluid synthesis; phenol hydrosilation; and arylhydrosilation.

In this embodiment, a hydride fluid of the formula

    M.sup.H D.sub.x D.sup.H.sub.y M.sup.H

where M^(H), D, D^(H), x and y are as defined above, by methods known tothose of ordinary skill in the art. The hydride fluid is then reacted byhydrosilation with a relatively small amount of a phenol, i.e., anamount less than needed to react with all the hydride sites on thehydride fluid, to produce a phenol-modified hydride siloxane of thegeneral formula

    M"D.sub.x D".sub.y M"

wherein each M" independently represents either a dialkyl hydrogensiloxy or a phenol-modified dialkyl siloxy; each D" independentlyrepresents either an alkyl hydrogen siloxy or a phenol-modified alkylsiloxy; provided the phenol-modified hydride siloxane has bothphenol-modified and hydride-modified siloxy groups; and D, x and y areas above defined.

The phenol-modified hydride siloxane is then reacted with an aryl in ahydrosilation reaction to produce the aryl-modified, phenol-modifiedsiloxanes of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following examples illustrate the present invention. They are not tobe construed to limit the scope of the claims in any manner whatsoever.

EXAMPLE 1 Hydride Fluid Synthesis

A hydride fluid of the general formula M^(H) D₁₀ M^(H) is prepared. 847grams of silicone tetramer and 153 grams of tetramethyl disiloxane areadded to a vessel and mixed. To the vessel is then charged 1 grams ofsulfuric acid and 5 grams of carbon black. The contents of the vessel isheated to 50° C. and held at that temperature for 3 hours. The mixtureis then heated to 100° C. for 1 hour and 5 grams of MgO is added to themixture. The resulting mixture is then filtered through Celite®545.

EXAMPLE 2 Eugenol Hydrosilation

727 grams of M^(H) D₁₀ M^(H) fluid of Example 1 is charged to a vessel.Separately, a mixture of 0.04 grams of platinum-based catalyst(Karstedt, U.S. Pat. No. 3,715,334) and 273 grams of eugenol isprepared. The Eugenol/platinum catalyst is then added to the M^(H) D₁₀M^(H) fluid at a rate to control the exotherm at less than 100° C. Thereaction mixture is mixed and checked for reaction completion. At thecompletion of the reaction, the light ends are stripped from the mixtureat 150° C. under 20 mm vacuum. The product has an average structure ofM^(Eu) D₁₀ M^(Eu).

EXAMPLE 3 Eugenol Hydride Fluid Synthesis

1000 grams of the M^(Eu) D₁₀ M^(Eu) from Example 2 is added to a vesselalong with 1000 grams of methyl hydrogen cyclics (containing less than0.1% of hexamethyl disiloxane). The vessel is then charged with 2 gramsof sulfuric acid and 10 grams of carbon black. The contents of thevessel is heated to 50° C. and held at that temperature for 3 hours. Themixture is then heated to 100° C for 1 hour and 10 grams of MgO is addedto the mixture. The resulting mixture is then filtered throughCelite®545 and contains a product having the average structure M^(Eu)D₁₀ D^(H) ₂₀ M^(Eu).

EXAMPLE 4 Phenyl Hydrosilation

504 grams of the M^(Eu) D₁₀ D^(H) ₂₀ M^(Eu) is added to a vessel. Tothis is added a mixture of 496 grams of α-methyl styrene and 0.03 gramsof platinum catalyst in 1000 grams of toluene at a rate to control theexotherm to below 100° C. The reaction mixture is stirred to completionand stripped to 150° C. pot temperature under 20 mm vacuum with an N₂purge to remove siloxane light-ends and toluene. The final product hasthe average structure of M^(Eu) D₁₀ D^(Ph) ₂₀ M^(Eu).

EXAMPLE 5

The procedures of Examples 1 to 4 are repeated to prepare a finalproduct having the average structure of M^(Eu) D₅₀ D^(Ph) ₁₀₀ M^(Eu).

EXAMPLES 6-7

The products of Examples 5 and 4, respectively, are tested for viscosityand refractive index. The results along with compositional data are setforth in Table 1 below.

                  TABLE 1                                                         ______________________________________                                        Example             6.sup.a 7.sup.b                                           ______________________________________                                        Composition, wt. %                                                            Eugenol             1.5     6.9                                               α-Methyl styrene                                                                            53.7    49.6                                              Total aromatic      55.2    56.5                                              Properties                                                                    Viscosity, centistokes                                                                            2938    588                                               Refractive Index @ 25° C.                                                                  1.5080  1.5040                                            ______________________________________                                         .sup.a = M.sup.Eu D.sub.50 D.sup.Ph M.sup.Eu                                  .sup.b = M.sup.Eu D.sub.10 D.sup.Ph100.sub.20 M.sup.Eu                   

From the data presented in Table 1, it can be seen thateugenol-terminated siloxanes having significantly improved refractiveindex can be prepared according to the present invention. It is notedthat typical refractive index values for polydimethylsiloxane is 1.4035at 25° C., and for eugenol-terminated siloxanes of the formula M^(Eu)D₁₀ M^(Eu) (Example 2) is on the order of 1.449 at 25° C.

The above-mentioned patents are hereby incorporated by reference.

Many variations of the present invention will suggest themselves tothose of ordinary skill in the art in light of the above-detaileddescription. For example, aromatics other than α-methyl styrene can bereacted with the eugenol hydride fluid to obtain compositions of thepresent invention. Further, the chain lengths, i.e., x and y, can varywidely within the preferred ranges. It is also contemplated that thehydrosilation with the aromatic compound can be run neat, i.e., withoutsolvent added. All such obvious modifications are within the fullintended scope of the appended claims.

We claim:
 1. A process for preparing an aryl-modified, phenol-modifiedsiloxane comprising:(a) preparing a hydride siloxane fluid of thegeneral formula:

    M.sup.H D.sub.x D.sup.H.sub.y M.sup.H

wherein M^(H) represents a dialkyl hydrogen siloxy unit, D represents adialkyl siloxy unit, D^(H) represents an alkyl hydrogen siloxy unit; xis above about 1 and y is above about 1; (b) reacting the hydridesiloxane fluid of step (a) with a phenol to produce a phenol-modifiedhydride siloxane of the general formula:

    M"D.sub.x D".sub.y M" ##STR3##  or a dialkyl hydrogen siloxy unit M.sup.H, defined above, where R.sub.a represents a divalent hydrocarbon radical of from 2 to about 12 carbon atoms, Y is selected from the group consisting of hydrogen, hydrocarbyl, hydrocarbyloxy and halogen, and R is an alkyl group having from 1 to about 10 carbon atoms; each D" independently represents either an alkyl hydrogen siloxy unit D.sup.H, defined above, or a phenol modified alkyl siloxy unit having the formula: ##STR4##  where R.sub.a, Y and R are as defined above, provided that there are both hydrogen containing siloxy units and phenol modified siloxy units in the phenol-modified hydride siloxane; and D, x and y are as defined above and

(c) reacting the phenol-modified hydride siloxane of step (b) with anaromatic compound to produce an aryl-modified, phenol-modified siloxaneof the general formula:

    M'D.sub.x D'.sub.y M'

wherein each M' independently represents a phenol-modified dialkylsiloxy group M", as defined above, or an aryl-modified dialkyl siloxygroup of the formula:

    R.sub.2 R.sup.AR SiO.sub. 1/2

wherein each R is as defined above and R^(AR) represents a monovalentaryl radical attached to the Si atom through an alkylene radical of atleast 2 carbon atoms; each D' independently represents a phenol-modifiedalkyl siloxy unit D", as defined above, or an aryl-modified alkyl siloxyunit having the formula

    RR.sup.AR SiO 2/2

where R and R^(AR) are as previously defined, provided that saidsiloxane comprises both phenol-modified siloxy units and aryl-modifiedsiloxy units, and D, x and y are as above defined, whereby saidaryl-modified, phenol-modified siloxane has a refractive index greaterthan about 1.5000.
 2. The process of claim 1 where x ranges from about 1to about 1,000 and y ranges from about 1 to about 2,000.
 3. The processof claim 2 where x ranges from about 5 to about 50 and y ranges fromabout 10 to about
 100. 4. The process of claim 1 wherein saidaryl-modified phenol modified siloxane has an aromatic content aboveabout 50 weight percent.